Walter Scott, Jr. College of Engineering

Graduate Exam Abstract

Tucker Kern
M.S. Final
May 13, 2014, 11:00 AM
Scott Bioengineering Odyssey Design Studio
Design of Integrated On-chip Impedance Sensors
Abstract: In this thesis two integrated sensor systems for measuring the impedance of a device under
test (DUT) are presented. Both sensors have potential applications in label-free affinity biosensors
for biological and bio-medical analysis. The first sensor is a purely capacitive sensor that operates
on the theory of capacitive division. Test capacitance is placed within a capacitive divider and
produces an output voltage proportional to its value. This voltage is then converted to a time-
domain signal for easy readout. The prototype capacitive sensor shows a resolution of 5 fF on
a base of 500 fF, which corresponds to a 1 % resolution. The second sensor, a general purpose
impedance sensor calculates the ratio between a DUT and reference impedance when stimulated
by a sinusoidal signal. Computation of DUT magnitude and phase is accomplished in silicon via
mixed-signal division and a phase module. An automatic gain controller (AGC) allows the sensor
to measure impedance from 30 Ω to 2.5 MΩ with no more than 10 % error and a resolution of
at least .44 %.
Prototypes of both sensing topologies were implemented in a .18 μm CMOS process and their
operation in silicon was verified. The prototype capacitive sensor required a circuit area of .014
mm2 and successfully demonstrated a resolution of 5 fF in silicon. A prototype impedance sensor
without the phase module or AGC was implemented with a circuit area of .17 mm2 . Functional
verification of the peak capture systems and mixed-signal divider was accomplished. The complete
implementation of the impedance sensor, with phase module and AGC, requires an estimated .28
mm2 of circuit area.
Adviser: Tom Chen
Co-Adviser: N/A
Non-ECE Member: Stuart Tobet
Member 3: Ali Pezeshki
Addional Members: N/A
Kern, T.; Chen, T., "A 0.18 μm integrated impedance sensor using a novel mixed-signal divider and automatic gain control," Circuits and Systems (ISCAS), 2014 IEEE International Symposium on, (in press)
Kern, T.; Chen, T., "A low-power, offset-corrected potentiostat for chemical imaging applications," Circuits and Systems (LASCAS), 2013 IEEE Fourth Latin American Symposium on,
Program of Study: